1. Field of the Invention
The present invention relates to modeling of the output drivers and, in particular, to modeling of the high-speed differential signals generated by the output drivers.
2. Discussion of Related Art
Modeling of circuits has been a staple of use for designing integrated circuits for quite some time. One such modeling software, SPICE, has been in use for nearly 40 years. The SPICE simulation models, such as IBIS, provide reasonable accuracy for applications of frequencies less than 200 MHz. The IBIS model is generated from SPICE models of the designed circuits and consist of I-V (Current-Voltage) response tables. The accuracy of these tables is defined by the current-voltage increment steps, usually about 100 mV.
However, in serializer/deserializer (SERDES) circuits, frequencies of above 1 GHz are commonly encountered. With frequencies above about 1 GHz, if the current-voltage increment is reduced to 4 mV, the I-V data generated by the IBIS model is a single-spaced table of data that is about 34 pages long. The limitation of the IBIS model is not only the size of the look-up table generated, but that the table is generated from a SPICE model designed for the circuit under test. The accuracy of the data in the table is therefore not as high as needed to provide acceptable prediction results for the circuit under test.
Therefore, there is a need for an ability to model the high-speed differential output of integrated circuits with specific accuracy of the device under test.